PHP errors appeared after a version change

Read the message rather than fear it

A PHP error message holds four pieces of information: the nature of the problem, the file, the line, and the chain of calls that led there. The file alone almost always names the culprit. If it sits in a module or theme directory, that component needs updating or replacing — not the CMS core, and not the PHP version.

The families of message are few. A function removed from the language produces a call-to-undefined-function error. A data type that became strict produces an argument error. Reading a value missing from an array, long tolerated, is now reported far more loudly. Those three cases cover the vast majority of breakages I meet.

Fix, replace, or step back

• Fix when the faulty code is yours: an override, a bespoke module, an adapted theme. The simplest and most durable case.
• Update when the component is maintained: the recent version is almost always compatible, and the problem goes away without writing a line.
• Replace when the component is abandoned: maintaining an unsupported module yourself costs more than it looks.
• Reverting to the previous version stays possible and immediate, but it is only extra time, not a solution.